Electrochemical and Mechanical Failure of Graphite-Based Anode Materials in Li-Ion Batteries for Electric Vehicles

Cheng Lin,Aihua Tang,Jilei Xing,Ningning Wu

doi:10.1155/2016/2940437

Cheng Lin, Aihua Tang + Show 2 more

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https://doi.org/10.1155/2016/2940437

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Abstract

Graphite-based anode materials undergo electrochemical reactions, coupling with mechanical degradation during battery operation, can affect or deteriorate the performance of Li-ion batteries dramatically, and even lead to the battery failure in electric vehicle. First, a single particle model (SPM) based on kinetics of electrochemical reactions was built in this paper. Then the Li-ion concentration and evolution of diffusion induced stresses (DISs) within the SPM under galvanostatic operating conditions were analyzed by utilizing a mathematical method. Next, evolution of stresses or strains in the SPM, together with mechanical degradation of anode materials, was elaborated in detail. Finally, in order to verify the hypothesis aforementioned surface and morphology of the graphite-based anode dismantled from fresh and degraded cells after galvanostatic charge/discharge cycling were analyzed by X-ray diffraction (XRD), field-emission scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The results show that large volume changes of anode materials caused DISs during Li-ion insertion and extraction within the active particles. The continuous accumulations of DISs brought about mechanical failure of the anode eventually.

Highlights

Li-ion cells are very compelling candidates for power supplies with their high-power and energy density and low selfdischarge rate
By a unique combination analysis of scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD), the results suggest that the mechanical failure of anode material can be caused by accumulated diffusion induced stresses (DISs) within active particles
This paper studied the evolution of stresses in a graphitebased anode of Li-ion batteries for EVs considering solid mechanics, diffusion theory, and electrochemical interfacial kinetics under galvanostatic condition

Summary

Introduction

Li-ion cells are very compelling candidates for power supplies with their high-power and energy density and low selfdischarge rate. Journal of Chemistry account for mechanical failure of active materials within the electrodes in batteries applied in EVs. Cheng and Verbrugge [4] recently analyzed the evolution of stress and strain energy due to DIS in a spherical insertion electrode particle under either galvanostatic or potentiostatic condition. The maximum stress increases with current density, radius of spherical particles, and lower Li-diffusivity in the electrode material, all of which lead to steeper concentration gradients between the surface and the core They were verified in literatures [6, 9,10,11]. The measurements from XRD reveal the lattice parameter changes, and SEM and TEM were applied to verify the microstructure differences of the graphitic nanoparticles between the fresh and degraded anodes These are the main contributions and are helpful to understand the DISs in this manuscript. The complex interplay between the origins and evolution of mechanical degradation and structure changes during electrochemical reaction in electrode materials were discussed

Single Particle Electrode Model

Evolution of Stresses within a SPM

Validation

Conclusions